I have an Undercover 'Smooth' on my 2010 Tundra and love it. I choose it for a few reasons.
1. It's light weight (under 70lbs.)
2. It's strong. It can hold around 300lbs.
3. You can paint it (unlike the original models)
4. 100% watertight. I drove it on the freeway for an hour in serious downpour and the bed was completely dry. I can wash the truck and no water gets in.
5. It goes off/on in minutes (seriously takes no more then 2-3 minutes)
6. Much less expensive then traditional fiberglass toppers. (paid right around $600 including shipping)
The downside is the added area I have to clean, especially a PITA when it comes time to wax/buff the truck